Electro-optical method and apparatus



April 30, 1940. P. BERNsTElN ELECTRO-OPTICAL METHOD AND APPARATUS FiledFeb. 2l, 1959 .mwN

INVENTOR L Aww/, w,

ATTORNEY Patented'v y.

PATENT ""oFFlca Emerso-or'rlcAnMarnop AND APPARATUS Philip Bernstein,Brooklyn, N. Y., assignor to Press Wireless, Inc., Chicago, lll., acorporation of Delaware Application February 21, 1939, Serial No.25"!,620

8 Claims.

This invention relates to electro-optical systems and moreparticularlyto systems for controlling the frequency and amplitude ofalternating current signalling waves. v

A principal object of the invention is to provide an improved form offrequency doubling and power level control systems.

Another principal object is to provide a novel form of level controlforwave signalling systems l generally.

A feature of the invention` relates to an improved method of convertingelectrical signalling voltages of one frequency to a voltage of adifferent frequency by using an oscillating cathodel ray beam.

Another feature relates to a frequency doubling system employing anoscillating cathoderay beam having means to limit the amplitude of thedoubled frequency.

A further feature relates to a system of electrooptical conversionemploying anoscillatory deilectable cathode-ray beam wherein the levelof the converted impulses is rendered substantially independent of theamplitude of the beam oscillation.

A further feature relates to a method of employing conventionalcathode-ray tube apparatus as a frequency converter in conjunction` witha graded light filter to compensate for uneq'ual amplitudes ofoscillation of the cathode-ray beam.

A still further feature relates to the novel organization, arrangementand relativelocation andinterconnection of parts which constitute animproved signal converter.

Other features and advantages noi'l specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.4

In the electrical communication arts, it is often highly desirable toconvert a signal WaveV of a given frequency into a wave of a multiple orharmonic frequency, or into a wave wherein the successive wave portionsare displaced by regularly recurrent periods. It is also advantageous insuch systems to be able to limit the power output of the system byproviding a suitable form of A. vV. C. or level control. These featuresare especiallyrusefulin radio communication systems where the effects oflevel variations in the carrier are to be overcome or compensated for.While therefore the present invention is susceptible of application toany signalling system wherein carrier frequency waves are employed, itis particularly useful in overcoming the effects of (Cl. Z50-20) fading,by providing an improved form of level control for the received signals.

In the drawing,

Fig. 1 is a schematic diagram of a portion of a wave signalling systemembodying features of the invention.

Fig. 21s an end view of the cathode-ray tubeof Fig. l.

Referring to the drawing which shows by Way of example one preferredembodiment of the invention,'only those parts of a typical radiosignalling system are shown to enable vthe inventive concept to be fullyunderstood, and parts and lconnections which are well-kown to thosefamiliar with the radio art are omitted. The numeral I represents anywell-known form of cathode-ray tube whether of the highly evacuated orgaslled type. n provided in the usual manner with an electron gun 3 ofknown construction for developing a focussed beam of electrons, wherebythe screen.A end of the tube is impinged upon by the focussed beam.Associated with the gun 2 are the usual deflecting systems comprisingfor example a pair of horizontal deflector plates 4, 5, and a pair ofvertical defiector plates 6; l. The enlarged flattened end of the tube'which is usually referred to as the screen is provided on its innersurface with any Well-known form of coating Which fluoresces underimpact of the cathode-ray beam from gun 3. Any well-known form of secondanode may be employed to accelerate the beam electrons from the guntoward the screen, and if desired the funnel-shaped part of the tube mayhave its interior surface coated with conducting material for thispurpose. The fluorescent screen may be either of the floating typeor itmay be electrically connected to a suitable potential as is well-knownin the cathode-ray tube art.

The signal to be converted is applied to the inputterminals 8, 9.Terminal 8 is connected directly to deflector plate 1, and terminal 9 isconnected to deflector plate 6 through a -beam biassing networkconsisting of the series resistor I0 which is shunted by the by-passcondenser I I, and the two resistors I2, I3. The biassing battery Il isalso adjustably connected to resistor IIJ to bias the cathode-ray beamso that normally it strikes approximately the central part of thescreen. Likewise the plates 4, 5, are connected to a biassing networkcomprising the resistors I4, I5, I6, and the biassing battery I1adjustably connected to resistance I4. By means of the two biassingnetworks therefore, the cathode-ray beam normally stays in one positionwhich is 'I'he neck portion 2 of the tube is I approximately on the axisof the tube, although as will be obvious, the normal position may be anyother desired position. Consequently, when a signalling wave, such forexample as an alternating current carrier wave, is impressed upon lterminals 8, 8, the beam is caused to oscillate so that it traces alinear path along a central vertical line of the tube screen.

Mounted adjacent the screen end of tube I, along the vertical centralportion thereof as shown in Fig. 2, is a light filter or light wedge I8of graded transparency from its lower edge I8 to its upper edge 20. Alsomounted in vertical alignment with member I8 is an opaque strip 2i, theupper edge 22 of which is slightly spaced from the adjacent edge I3 ofstrip I8, thus deflning a gap 23 of a gap-width approximately the sameas the vertical dimension of the cathode-ray beam where it strikes thescreen. If desired, the strips I8 and 2| may be cemented or otherwisefas-` tened to the end of tube I or in certain cases they may be in theform of coatings or the. glass of the tube itself may be treated toprovide the requisite transparency or opaqueness.

Mounted in optical alignment with the gap 23 is a lens system 24 whichimages upon a light sensitive cell 25, the light of the iluorescentscreen which passes through gap 23. The cell 25 is provided with anysuitable coupling circuit 26 whereby it is coupled to the amplifier tube21. Also mounted in optical alignment with the strip I8 is a lens system28 which images the light passed by the strip I8 on another lightsensitive cell 29 which is provided with a suitable coupling circuit 30for coupling to the amplifier tube 3|. The output of amplier tube 3| isapplied through a conventional resistance coupling arrangement as shown,to the rectier tube 32 and the rectied output of tube 32 produces acorresponding potential drop across the resistor 33. Resistor 33 isconnected in series with another resistor 3l and a suitable grid biasbattery to the grid 35 of tube 21 the resistor 33 is a common loadresistor for the cathodes of tube 32 and for the control grid 35 of tube21 whereby the gainof course, that suitable potentials are applied to,

the various electrodes of tube 2,1. For example the control-grid 'may bebiassed by the biassing arrangement Il to a potential of approximately-3 volts; the grids 38 and 39 may be connected to a positive potentialof the order of 100 volts; the anode 42 may be connected to a positivepotential of the o'rder of 250 volts although it will be understood thatthese voltages are merely typical. With this arrangement therefore, the

'iiuorescent light signals which are picked up by the cell 25 areconverted into potentials which are impressed on grid 31 and result incorresponding amplified voltages across the output resistor 33 :I'helevel or gain of the Voutput of tube 21 is controlled by the negativepotential on grid 35 which in turn is determined by the voltage dropacross resistor 33. Aspointed out above. the voltage drop acrossresistor 33 is determined by the signal picked up by the iight sensitivecell 23. It will be obvious therefore. that the gain of the tube 21 willdepend 'upon the amplitude o! oscillation of the cathode-ray beam. Thus,if the beam has its minimum amplitude,v it does not go beyond therelatively dense portion of the strip I8 with the result that apredetermined negative potential is applied to grid 35. As the amplitudeof the cathode-ray beam oscillation increases, a correspondingly greateramount o! light is passed by the strip I8 resulting in a correspondingdecrease in the negative grid biassing potential on the gain controlgrid 35.

So long as the amplitude of the cathode-ray beam remains constant, theoutput level of tube 21 likewise remains constant. However, each timethat the beam traverses the gap 23, an impulse is produced in the outputof tube 21. Consequently, for each complete cycle of input signalapplied to terminals 8` and 8, the cathode-ray beam traverses the gap 23twice, thus doubling the frequency of the signal in the output of tube21 as compared with the frequency of the signal impressed on terminals 8and 8.

Since the cathode-ray beam is not subjected to any intensity control,the luminescent spot remains of substantially constant intensity.However, when the amplitude of oscillation of the beam is increased, thevelocity of the beam across the gap 23 is likewise increased whichreduces the duration of the impulses in the output circuit of tube 21with a corresponding decrease in the power output of the tube. On theother hand, for smaller amplitudes the power output of tube 21 wouldtend to correspondingly increase. 'Ihe purpose of the graded densitystrip I8 and the cell 29 together with the tubes 3I and 32 is tocompensate for this tendency to change in level of the output ofamplifier 21. The density lter I8 as above described is so constructedas to efiect a variation in light intensity to cell 23 which is indirect relation to the amplitude of the beam oscillation. -However, thegreater this amplitude of oscillation, the greater is the amount ofcurrent rectified by tube 32 which acts as above described as a "volumeexpander for the output of tube 21, by decreasing the negative bias on35 in direct relation to the amplitude of the cathode-ray beamoscillation and correspondingly increasing the gain and power output oftube 21. By properly designing the density iilter as regards its densitygradations from one end to the other, a linear power output can beproduced for the entire system.- Consequently, the output of amplifier-21 can then be set at any desired value and will remain. substantiallyxed regardless of the variation in level of the waves applied toterminals 8 and 9. l

While one specific embodiment of the invention has been disclosedherein, it will be understood that various changes and modifications maybe made therein without departing from the spirit and scope of theinvention. For example,

while the cathode-ray beam is shown as being.'

oscillated by electrostatic deector means, it will y be understood thatthe beam may be deilected by magnetic means or by a combination ofmagnetic and electrostatic means. For example, the horizontal plates land 5 may be replaced by a suitable electromagnet for biassing the beamto its central position and the vertical deflection of the beam undercontrol of the signals may be done by the electrostatic plates 6 and 1.Fur- 1| 'the beam, it will be understood of course, that any well-knownform of modulatingy electrode such as a grid may be provided inconnection with the electron gun so as to modulate the intensity of thebeam. Thus, for example, a carrier current may be applied to theterminals-8, 9, and modulating potential signals may be applied to thecontrol-grid or modulating-grid in the tube 2. Furthermore, while thedisclosure relates to the doubling of an input frequency by using oneaperture, a plurality of apertures may be employed to produce anyharmonic of the input frequency. Likewise, while the description isbased upon a linear traverse of the Acathoderay beam, it will beunderstood that the beam may be caused to traverse any fixed path, e.g., circular or elliptical or any other shape path well-known in thecathode-ray art so long as the beam traverses one or more apertures andis provided with a graded density member for producing a compensatingsignal in proportion to the amplitude of the beam movement.`

What I claim is:

l. The metliod of wave signalling systems which includes the steps ofelectro-optically converting electric signal waves into other electricsignal waves of a multiple frequency, and electrooptically producingunder control of the first waves a level control signal for theconverted waves.

2. In a wave signalling system, means to de velop a deflectable beam,electro-optical means for producing electric signals under control ofsaid beam, and electro-optical means for producing level control signalsfor said electric signals.

3. In a wave signalling system, means to develop a beam of electrons,means to oscillate said beam under control of input signals, meanscontrolled by said beamv for producing electric signais of a frequencydifferent from said input signals, and means controlled by the amplitudeof the beam oscillations'for controlling the level of thesecond-mentioned signals.

4. A wave signalling system according to claim 3 in which the means forproducing said signals of different frequency includes a fluorescentscreen upon which the beam impinges and an aperture and light sensitivecell, the cell being energized by the fluorescence of said screenthrough said aperture.

5. A wave signallingsystem according to claim 3 in which the means forcontrolling the level v of the said second signals includes a gradeddensity member and a light sensitive cell, the cell being mounted so asto be energized by said beam through said graded density member.

6. A frequency converter for wave signals which includes a cathode-raytube having means to develop a cathode-ray beam and means to defiect thebeam in accordance with input signals; a fluorescent screen upon whichthe beam impinges; a light sensitive cell mounted so as to be energizedonly when a predetermined area of said screen is fluorescent; anotherlight sensitive cell; and means between said other cell and screen forenergizing said other cell in proportion to the amplitude of thebeamoscillations.

7. A frequency converter and power limiter for wave signalling systemscomprising a cathoderay tube, means to deflect the cathode-ray beamalong a predetermined path under control of input signals,electro-optical means controlled by the beam for producing outputsignals having a frequency which is a multiple ofthe input signals,

electro-optical means controlled by the beam amplitude for rproducinglevel control signals, an amplifier for said output signals, and a gain`control circuit for controlling the level of said amplifier, said gaincontrol circuit being controlled by said level control signals.

8. A frequency multiplier and power limiting device for wave signallingsystems comprising a cathode-ray tube having a fluorescent screen. a

-light aperture adjacent said screen, a graded density member alsomounted adjacent said screen, and a pair of light sensitive cells, onein optical alignment with the said aperture and the other in opticalalignment with said graded density member.

PHILIP BERNSTEIN.

